The present paper describes an experimental study on the flow dynamics within a centrifugal pump impeller. A transparent pump prototype made of acrylic parts was firstly developed for flow visualization purposes. Then, single-phase flow experiments were conducted in different impeller rotational speeds and water flow rates. A time-resolved particle image velocimetry (TR-PIV) system was used as the flow visualization method. As a result, velocity fields were obtained in the whole impeller. They reveal that the flow behaviour is dependent on the pump operational condition. When the pump works at the best efficiency point (BEP), the flow is uniform and the streamlines follow the blade curvature. However, when the machine works at off-design conditions, the flow becomes complex, with the presence of turbulent structures which cause a reduction in the pump performance. This type of result may be useful to validate numerical simulations and support the proposition of new mathematical models, new impeller geometries, among other applications.
Tag: centrifugal pump
A novel criterion based on slip ratio to assess the flow behavior of W/O emulsions within centrifugal pumps
Water-in-oil emulsions usually present complex rheological behavior that depends on the physicochem-ical properties of both phases, the presence of surfactants, and the flow conditions. Thereby, this paperaims to propose a criterion to characterize the rheological behavior of stable and unstable water-in-oil emulsions within the centrifugal pumps. This criterion is based on the slip ratio between the dispersedand continuous phases. For this, the droplet size distribution was measured at the ESP outlet and the slipratio was estimated based on the centrifugal buoyancy-induced flow. A new model was proposed todetermine the Sauter mean diameter for different systems of the water-in-oil emulsion flows withinthe ESP based on operational conditions, which presents good agreement with the experimental data(12.6% of error). Finally, a new dimensionless number parameter named Slip Relevance number was pro-posed to separate the different emulsion flow behaviors within the ESP and its critical value was obtained.
Flow visualization in centrifugal pumps: A review of methods and experimental studies
Methods for flow visualization have been decisive for the historical development of fluid mechanics. In recent years, technological advances in cameras, lasers, and other devices improved the accuracy and reliability of methods such as High-Speed Imaging (HSI) and Particle Image Velocimetry (PIV), which have become more efficient in visualizing complex transient flows. Thus, the study of centrifugal pumps now relies on experimental techniques that enable a quantitative characterization of single- and two-phase flows within impellers and diffusers. This is particularly important for oil production, which massively employs the so-called Electrical Submersible Pump (ESP), whose performance depends on the behavior of bubbles and drops inside its impellers. Visualization methods are frequently used to study gas-liquid flows in pumps; however, the visualization of liquid-liquid dispersions is complex and less common, with few publications available. Methods to characterize the motion of gas bubbles are often unsuitable for liquid drops, especially when these drops are arranged as emulsions. In this context, there is room to expand the use of visualization techniques to study liquid-liquid mixtures in pumps, in order to improve the comprehension of phenomena such as effective viscosity and phase inversion with focus on the proposition of mathematical models, for example. This is a main motivation for this paper, which presents a review of researches available in the literature on flow visualization in centrifugal pumps. A broad set of studies are reported to provide the reader with a complete summary of the main practices adopted and results achieved by scientists worldwide. The paper compares the methods, investigates their advantages and limitations, and suggests future studies that may complement the knowledge and fill the current gaps on the visualization of single-phase flows, gas-liquid, and liquid-liquid mixtures.
Experimental analysis on the behavior of water drops dispersed in oil within a centrifugal pump impeller
This paper aims to investigate the behavior of water drops in an oil continuous medium inside a centrifugal pump impeller working at eight operational conditions (up to 1200 rpm and 2.8 m³/h) with two-phase liquid-liquid flows. Water-in-oil dispersions were produced with low water fractions around 1% in volume, thus the dispersed phase became arranged as water drops. Experiments for pump performance and flow visualization were conducted using a high-speed camera and a pump prototype with a transparent shell. Flow images revealed that the large water drops usually deform, elongate, and break up into smaller ones, especially at high pump rotations and oil flow rates, while small water drops tend to keep their spherical geometry without deformations and fragmentations. A sample of drops were tracked and their equivalent diameters, residence times, and velocities were calculated. The tracking indicated that the water drops travel random trajectories in the channels, generally undergoing a deceleration along their pathway. Furthermore, the residence times and the average velocities of water drops strongly depend on the flow conditions. For the conditions tested, the water drops presented equivalent diameters between 0.1 and 6.0 mm, average velocities from 0.4 to 1.7 m/s, and residence times between 30 and 152 ms. For a more complete analysis, the results achieved in this study are constantly compared with results available in literature regarding oil drops in oil-in-water dispersions.
Experimental Investigation of Oil Drops Behavior in Dispersed Oil-Water Two-Phase Flow within a Centrifugal Pump Impeller
In oil production, one important artificial lift method involves the commonly used centrifugal pump. The use of this pump in the petroleum industry, however, is hindered by some unfavorable operational conditions. Operating centrifugal pumps with gas and viscous fluids, such as dispersions, may lead to a degradation of their performance. The objective of this paper is to analyze oil-water dispersions in a pump impeller, in order to investigate the behavior of oil drops, which may influence the pump working. Thus, experiments were carried out at different pump rotation speeds and water flow rates. Researchers used a facility with a pump prototype that enabled them to visualize the flow in all the impeller channels. Images, captured through a high-speed camera, revealed a unique flow pattern of oil drops dispersed in water. Processed with computer codes, the images indicated that the oil drops were, in general, spherical or elliptical, and only a few broke up in the impeller. The interaction with water caused the oil drops to rotate, deform, and deviate, thus moving in random paths. Size distributions suggested that the drops became smaller as the impeller rotation speed and water flow rate increased. This behavior was due to the turbulence-induced shear stress and kinetic energy. The oil drops’ equivalent diameters ranged from 0.1 to 6.0 mm; velocities took values measurable by units of m/s; accelerations reached hundreds of m/s2; and forces had magnitudes of thousandths of N. Researchers observed a clear dependence between flow conditions and drop dynamics. Carried by the water flow, the oil drops on the suction blade moved faster than those on the pressure blade of a channel. The drop dynamics were significantly influenced by the presence of adverse pressure gradients and water velocity fields.
Experimental and Numerical Study of Oil Drop Motion within an ESP Impeller
The Electrical Submersible Pump (ESP) is a multistage centrifugal pump used in the petroleum industry as an artificial lift method. The ESP usually works with the presence of two-phase liquid-liquid flows that constitute dispersions and emulsions, causing performance losses and operational problems. This research aims to investigate the behavior and evaluate the dynamics of individual oil drops in an oil-in-water dispersion within an ESP impeller. The study adopts experimental and numerical approaches. Initially, experiments were performed using an experimental facility with a high-speed camera and an ESP prototype working at 600 rpm and 900 rpm, for water flows around the Best Efficiency Point (BEP) and with the injection of oil drops at a low flow rate. The acquired images were processed, and a drop sample was tracked, enabling the analysis of the size, shape, path, velocity, and acceleration of the oil drops. Numerical simulations were executed in ANSYS® software to define relevant parameters related to water and oil drops, such as velocities, accelerations, forces, turbulent dissipation, and residence time. The images reveal a unique flow pattern of dispersed drops in a continuous water phase. The oil drops’ diameters vary from tenths of a millimeter to around 3 mm. The drops’ trajectories can be classified into three different regions within the impeller channels. The drops’ velocities stay in the order of 1 m/s, while accelerations can reach hundreds of m/s2. The velocity profiles show that the oil drops tend to decelerate during their trajectory, while the acceleration profiles suggest peaks at the channel inlet and outlet. High intense turbulence is present in the impeller entrance zone. The evaluation of the residence time and the particle Reynolds number suggest that smaller oil drops follow the water streamlines, while larger oil drops tend to be affected by external forces. The main forces that govern the oil drop motion are the drag, the pressure gradient, and the virtual mass forces. The force from the pressure gradient is tenfold greater than the force from the drag. The virtual mass effect is significant only in the impeller inlet. In general, in this research, numerical results show a satisfactory agreement with the experimental data.
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